Vacuum control system



Feb. 5, 1952 Filed Sept. 1,1949

A; TOR

Patented Feb. 5, 1952 VACUUM CONTROL SYSTEM Wheaton W. Kraft, Scarsdale, N. Y., assigner to The Lummus Company, New York, N. Y., a corporation of Delaware Application september 1, 1949, serial No. 113,535

(c1. 2oz-52) 6 Claims.

This invention relates to dlstillationand more particularly` to a method o f controlling the pressure in a vacuum tower.

Control of vacuum distillation is primarily a matter of regulating the pressure in the tower. It is well known in the distillation art that a change of pressure will affect the bubble point of a liquid and the composition of the vapor given off by the liquid. It is very important therefore to obtain constancy of operation in order to have fixed and predetermined products taken off from the tower in the various cuts.

When a barometric condenser and attached steam jets are used to produce a vacuum, the system is normally operated at maximum capacity, with full steam to primary and secondary jets. The water dow to the barometric leg is regulated to produce the optimum setting; thus there is no margin on which to draw in order to minimize uctuations which result from changes in water temperature.

Due to unusual weather conditions, cooling water temperatures may change as much as or F. during a twenty-four hour period. This change may be gradual over the course of a day or itmay be sudden, as for instance, when there is a rain-storm. Changes in water temperature cause a corresponding change in pressure at the top of the distillation tower. Variations of as much as twenty millimeters of mercury have been observed. This is too great a deviation from the normal vacuum tower pressure which may be fty millimeters of mercury.'

Tower conditions are seriously affected by these fluctuations and repeated adjustments in tower top temperatures and off-take settings are necessary.

Objects and advantages of my invention will be apparent from the following description thereof taken in connection with the accompanying drawing which is a iiow sheet of the vacuum producing equipment as used in connection with a petroleum vacuum distillation tower.

The principal feature of my invention resides in the use of a control system which is capable of being set to maintain a given pressure at the top of the tower. This pressure preferably corresponds to the vapor pressure of water at the maximum water temperature to be expected, generally not over 90 F. In a standard unit as normally operated, the flow of water to the condensing and vacuum apparatus at the top of the tower may consist of a common inlet line dividing to feed the barometric condenser and the vapor condenser separately. The water in the barometric tail pipe may contain entrained oil and it may be at a lower temperature than the outlet of the vapor condenser. Except for a common water feed there is no intersection or connection between the vapor condenser and the barometric condenser.

According to my invention as shown in Fig. 1, a vacuum tower I2 is shown having a vapor condenser I4 preferably mounted as indicated but which may be located external to the tower. A barometric condenser I6 is located near the top of the tower and draws evacuated gases from tower I2 through line I8. Both vapor condenser I4 and barometric condenser IB are fed cold. water from line 28 shown as a common line.

Barometric condenser I6 is normally fed water from line 20, line 22, through three-way valve 24, and line 26. Water is discharged through line 28. Steam ejectors, not shown, are attached to barometric condenser I6 in a manner well known to the art.

Vapor condenser I4 is normally fed cold water from line 20 through line 30. Warm water discharges through line 32. valve 42, and line 34 when the unit is operating under normal conditions.

A warm water by-pass line 36 is supplied connecting the outlet line 32 of vapor condenser I4 to the inlet line 26 to barometric condenser I6 by means of a three-way valve 24 hereinbefore referred to.

Three-way valve 24 is controlled by a temperature controller 38, preferably, but not necessarily, an indicating instrument of the bulb type. Controller 38 is connected to valve 24 through signal transfer line 48. Temperature controller 38 will be installed in the tail pipe 28 of the barometric condenser I6 as shown, where it can measure the outlet temperature of the water.

A throttle valve 42 installed in line 34 is controlled by a liow control 44 preferably of the differential mechanical type with indicating attachment. Flow control 44 responds to the flow through orifice 46 and transmits this information to valve 42 through signal transfer line 48.

The barometric condenser is designed to operate at the highest average temperature of available cooling water generally not above F. Vapor condenser I4 is designed to operate with a fixed water rate. Normal conditions are defined as those existing in the barometric condenser I6 and tower I2 when the water is at the-highest average temperature. The design vacuum will then be produced in line I8 and tower I2.

The suitable operation of barometric condenser crease due to increased back pressure.

assegni I6 depends upon three factors: (1) the tail pipe temperature must be maintained constant, (2) a substantial amount of water must be fed to the unit to keep it within its proper operating range, 3) the duty of the unit must be constant. Tins means that if the temperature of the inlet water drops, thereby necessitating a larger temperature rise, then a somewhat smaller amount of water is necessary.

According to my invention, when there occurs a change in tower pressure resulting from a decrease in water temperature, controller 38 will respond to the change in tail-pipe temperature. A signal will be transmitted from controller 38 through line 40, which will adjust valve 24 permitting warm water from vapor condenser outlet 32 to pass through line 36 and valve 24, and cutting down on the amount of cold water passing through line 22. This warm water will mix with the cold water entering from lines 20 and 22 and in this manner fluctuations in water temperature can be minimized.

As the quantity of water passing through line 22 decreases, the ilow in line 3l) will tend to in- However orifice 46 and flow control 44 may be so designed that a constant flow of water is passed to vapor condenser I4 if desired. As the larger amount of water passes through orifice 46, the larger pressure drop across the orifice actuates the iiow control 44 which transmits a signal through line 4B to valve 42. This valve 42 will close and by virtue of the back pressure which it puts on the system will decrease the pressure drop through the orifice 46 thereby controlling the quantity of water to condenser I4.

While I have shown and described a preferred form of embodiment of my invention, I am aware that variations may be made thereto and I therefore desire a broad interpretation of my invention within the scope of the disclosure herein and the following claims.

I claim:

1. A method of operating a vacuum distillation system having a vacuum distillation tower, a barometric condenser attached thereto, and a vapor condenser to maintain a constant vacuum in the distillation tower, said method comprising the steps of passing fresh cooling water to the barometric condenser, passing fresh cooling water to the vapor condenser, withdrawing said water from the barometric condenser', determining the temperature of thc water withdrawn from the barometric condenser, regulating the passing of `fresh cooling water to the barometric condenser in accordance with said temperature determination, withdrawing warm water from said vapor condenser, bypassing a variable portion of said withdrawn Warm water to the barometric condenser, concurrently regulating said bypassing of warm Water in accordance with said temperature determination, thereby controlling both the temperature and quantity of water passed to the barometric condenser.

2. The method of claim l in which the temperature of the water withdrawn from the barometric condenser and the duty of said barometric condenser are maintained constant.

3. A method of operating a vacuum distillation system having a vacuum distillation tower, a barometric condenser attached thereto, and a vapor condenser to maintain a constant vacuum in the distillation tower, said method comprising the steps of passing fresh cooling Water to the barometric condenser, passing fresh cooling water to the vapor condenser, withdrawing said water from the barometric condenser, determining the temperature of the water withdrawn from the barometric condenser, regulating the passing of fresh cooling water to the barometric condenser in accordance with said temperature determination, withdrawing warm water from said vapor condenser, bypassing a portion of said withdrawn Warm Water to the barometric condenser, concurrently regulating said bypassing of warm water in accordance with said temperature determination, determining the flow of fresh cooling water passed to the vapor condenser, and regulating the warm water withdrawn from the vapor condenser ahead of the point of bypassing in accordance with said flow determination to maintain a constant fiow of water through the vapor condenser.

4. The method of claim 3 in which the temperature of the water withdrawn from the barometric condenser and the duty of the barometric condenser are maintained constant by said regulating steps.

5. An apparatus for maintaining a constant pressure in a vacuum tower which comprises a vapor condenser at said tower, a barometric condenser adapted to create a vacuum in said tower, inlet means to pass fresh cooling water to said vapor condenser, inlet means to pass fresh cooling water to said barometric condenser, by-pass means to pass warm water from said vapor condenser to a junction with the inlet means of said barometric condenser, flow control means at said junction, outlet means from said barometric condenser, means responsive to the temperature of the water in said outlet means from said barometric condenser, means for generating a signal corresponding to said temperature, means for transmitting said signal to said control means at said junction thereby causing said control means to change the relative amounts of fresh cooling water and warm water passed to said barometric condenser thereby adjusting the tem-- perature, and independent outlet means for said vapor condenser.

6. An apparatus for maintaining a constant pressure in a vacuum tower which comprises a vapor condenser at said tower, a barometric condenser adapted to create a vacuum in said tower, inlet means to pass fresh cooling water to said vapor condenser, inlet means to pass fresh cooling Water to said barometric condenser, by-pass means to pass warm water from said vapor condenser to a junction with the inlet means of said barometric condenser, flow control means at said junction, outlet means from said barometric condenser, means responsive to the temperature of the water in said outlet means from said barometric condenser, means for generating a signal corresponding to said temperature, means for transmitting said signal to said control means at said junction, thereby causing said control means to change the relative amounts of fresh cooling water and warm water passed to said barometric condenser and thereby adjust the temperature. independent outlet means for said vapor condenser, ow control means capable of controlling the flow in said independent outlet means, means responsive to the flow of fresh cooling water in said inlet means to said vapor condenser, means for generating a signal corresponding to said flow, and means for transmitting said signal to the now control means in said independent outlet means from said vapor condenser whereby 5 the quantity of water passing through said vapor Number condenserl may be controlled as desired. 1,427,626 WHEATON W. KRAFT. 1,575,031 1,630,767 REFERENCES CITED 1,706,719 The following references are'of record in the 2,167,028 me of this patent: 1341281 UNITED STATES PATENTS Number l Name Date Number 405,142 Worthington June 11, 1889 343,982

Name Date Owen Aug. 29, 1922 Bell Mar. 2, 1926 Schmidtl May 31, 1927 Ware Mar. 26, 1929 McGovern July 25, 1939 McGovern Feb. 8, 1944 FOREIGN PATENTS Country Date Great Britain Dec. 10, 1925 

